The present invention deals with implantable medical devices. While conceivably the devices could be utilized in the context of a variety of body spaces, the present description, for the sake of brevity, will often be described in the context of the treatment of vascular aneurysms. Accordingly, one aspect of the present invention deals with an implantable medical device for at least partially obstructing a vascular aneurysm.
Another aspect of the present invention pertains to a medical device for forming an embolism within the vasculature of a patient. More particularly, the invention pertains to vaso-occlusion devices at least partially coated with a bioactive agent, an absorbable material and/or a biopolymer or an absorbable biopolymer coating optionally containing  or coated with other bioactive agents. A highly flexible vaso-occlusive device coated with such materials also forms a variation of the invention.
Vascular aneurysms are typically formed due to a weakening in the walls of an artery. Often aneurysms are the site of internal bleeding and, catastrophically, the site of strokes. Different implantable medical devices have been developed for treating vascular aneurysms. Treatments commonly known as “artificial vaso-occlusion” treatments are known to be useful in treating aneurysms by filling associated undesirable vascular spaces. A variety of different vaso-occlusive devices are known to be at least arguably effective for the treatment of aneurysms.
Vaso-occlusive devices are surgical implants that are placed within open sites in the vasculature of the human body. The devices are introduced typically via a catheter to the site within the vasculature that is to be closed. That site may be within the lumen of a blood vessel or perhaps within an aneurysm stemming from a blood vessel.
There are a variety of materials and devices that have been used to create emboli in the vasculature of the human body. For instance, injectable fluids such as microfibrillar collagen, various polymeric foams and beads have been used. Certain injectable fluid devices can be introduced through a catheter and are capable of forming a solid  space-filling mass in a target location. Polymeric resins, particularly cyanoacrylate resins, have been used as injectable vaso-occlusive materials. Both the injectable gel and resin materials are typically mixed with a radio-opaque material to allow accurate setting of the resulted materials. Although some of these agents provide for excellent short-term occlusion, many are thought to allow vessel recanalization due to absorption of the agents into the blood. In addition, there are significant risks involved in use of cyanocrylates, and similar materials, due to the potential for misplacement. Such misplacement can create emboli in undesired areas. Generally, injectable fluid occlusion devices are somewhat difficult, if not impossible, to retrieve once they are improperly placed.
In some instances, materials such as hog hair and suspensions of metal particles have been introduced into an aneurysm by those wishing to form occlusions. It is believed that these materials encourage natural cell growth within the sac portion of an aneurysm.
Several patents describe different deployable vaso-occlusive devices that have added materials designed to increase their thrombogenicity. For example, fibered vaso-occlusive devices have been described in patents assigned to Target Therapeutics, Inc., of Fremont, Calif. Vaso-occlusive coils having attached fibers are shown in U.S. Pat. Nos.  5,226,911 and 5,304,194, both to Chee et al. Another vaso-occlusive coil having attached fiberous materials is found in U.S. Pat. No. 5,382,259, to Phelps et al. The Phelps et al. patent describes a vaso-occlusive coil which is covered with a polymeric fiberous braid on its exterior surface. U.S. Pat. No. 5,658,308, to Snyder, is directed to a vaso-occlusive coil having a bioactive core.
To further increase occlusive properties and thrombogenicity, a variety of vaso-occlusive devices have been treated with a variety of substances. For instance, U.S. Pat. No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded, convoluted configuration when relaxed. The stretched condition is used in placing the coil at the desired site (via passage through the catheter) and the coil assumes a relaxed configuration—which is better suited to occlude the vessel—once the device is so-placed. Ritchart et al. describes a variety of shapes. The secondary shapes of the disclosed coils include “flower” shapes and double vortices. The coils may be coated with agarose, collagen, or sugar.
U.S. Pat. No. 5,669,931, to Kupiecki, discloses coils that may be filled or coated with thrombotic or medicinal material. U.S. Pat. No. 5,749,894, to Engelson, discloses polymer-coated vaso-occlusion devices. U.S. Pat. No. 5,690,671 to  McGurk discloses an embolic element which may include a coating, such as collagen, on the filament surface.
U.S. Pat. No. 5,536,274 to Neuss shows a spiral implant which may assume a variety of secondary shapes. Some complex shapes can be formed by interconnecting two or more of the spiral-shaped implants. To promote blood coagulation, the implants may be coated with metal particles, silicone, PTFE, rubber lattices, or polymers.
Advancements in the artificial occlusion of aneurysms have occurred due to the delivery and implantation of metal coils as vaso-occlusive devices.
Vaso-occlusion coils are generally constructed of a wire, usually made of a metal or metal alloy, which is wound into a helix. Most commonly, these coils are introduced in a stretched linear form through a catheter to the selected target site, such as a particular aneurysm. The vaso-occlusion coils typically assume an irregular shape upon discharge of the device from the distal end of the catheter. The coils may undertake any of a number of random configurations used to fill an aneurysm. In some instances, vaso-occlusion coils are adapted to assume a predetermined secondary shape designed to enhance the ability to fill undesirable vascular spaces.
A variety of vaso-occlusion coils and braids are known. Tungsten, platinum, and gold threads or wires are said to be preferred. Vaso-occlusion coils have  a variety of benefits including that they are relatively permanent, they may be easily imaged radiographically, they may be located at a well defined vessel site, and they can be retrieved.
In some instances, particularized features of coil designs, such as specialized mechanisms for delivering vaso-occlusion coils through delivery catheters and implanting them in a desired occlusion site, have been described. Examples of categories of vaso-occlusion coils having specialized delivery mechanisms include pushable coils, mechanically detachable coils, and electrolytically detachable coils.
Pushable coils are commonly provided in a cartridge and are pushed or plunged from an engaged delivery catheter into an aneurysm. A pusher wire advances the pushable coils through and out of the delivery catheter into the site for occlusion.
Mechanically detachable vaso-occlusive devices are typically integrated with a pusher wire and are mechanically detached from the distal end of that pusher wire after exiting a delivery catheter.
A variety of mechanically detachable devices are also known. For instance, U.S. Pat. No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having an interlocking surface. U.S. Pat. No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps that are mounted both on the pusher and on the  embolic coil. U.S. Pat. No. 5,261,195, to Twyford et al., shows a pusher-vaso-occlusive coil assembly having an affixed, proximately extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengaged when expelled from the distal tip of the catheter. U.S. Pat. No. 5,312,415, to Palermo, also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil. U.S. Pat. No. 5,350,297, to Palermo et al., shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil.
Within electrolytically detachable vaso-occlusive devices, the vaso-occlusive portion of the assembly is attached to a pusher wire via a small electrolytically severable joint. The electrolytically severable joint is severed by the placement of an appropriate voltage on the core wire. The joint erodes in preference either to the vaso-occlusive device itself or to the pusher wire. In accordance with principles of competitive erosion, parts of the wire that are not intended to erode are often simply insulated to prevent such an  electrolytic response caused by the imposition of the electrical current.
U.S. Pat. No. 5,354,295 and its parent U.S. Pat. No. 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device. That is to say that a joint between the pusher wire and the vaso-occlusive portion dissolves or erodes when an electrical current is applied to the pusher wire.
Some vaso-occlusive devices include specialized mechanical features and/or shapes. Various shaped coils have been described. For example, U.S. Pat. No. 5,624,461, to Mariant, describes a three-dimensional in-filling vaso-occlusive coil. U.S. Pat. No. 5,639,277, to Mariant et al., describes embolic coils having twisted helical shapes and U.S. Pat. No. 5,649,949, to Wallace et al., describes variable cross-section conical vaso-occlusive coils. A random shape is described, as well. U.S. Pat. No. 5,648,082, to Sung et al., describes methods for treating arrhythmia using coils which assume random configurations upon deployment from a catheter. U.S. Pat. No. 5,537,338 describes a multi-element intravascular occlusion device in which shaped coils may be employed. Spherical shaped occlusive devices are described in U.S. Pat. No. 5,645,558 to Horton. Horton describes how one or more strands can be wound to form a substantially hollow spherical or ovoid shape when deployed in a vessel. U.S. Pat. Nos. 5,690,666 and 5,718,711, by Berenstein et al., show a  very flexible vaso-occlusive coil having little or no shape after introduction into the vascular space.
One type of aneurysm commonly known as a “wide-neck aneurysm” is known to present particular difficulty in the placement and retention of vaso-occlusive devices. Furthermore, vaso-occlusive devices, in particular, vaso-occlusion coils, lacking substantial secondary shape strength may be difficult to maintain in position within an aneurysm no matter how skillfully they are placed.
Vaso-occlusive devices are typically placed in an aneurysm in the following fashion. A micro-catheter is initially steered into or adjacent the entrance of an aneurysm, typically aided by the use of a steerable guide wire. The guide wire is then withdrawn from the micro-catheter and replaced by the vaso-occlusive device. The vaso-occlusive device is advanced through and out of the micro-catheter, desirably being completely delivered into the aneurysm. After, or perhaps, during, delivery of the device into the aneurysm, there is a specific risk that the device or a portion of the device might migrate out of the aneurysm entrance zone and into the feeding vessel. The presence of the device in the feeding vessel may cause the undesirable response of an occlusion in the feeding vessel. Also, there is a quantifiable risk that blood flow in the feeding vessel and the aneurysm may induce movement of the  device further out of the aneurysm, resulting in a more developed embolus in the patent vessel.
As noted above, aneurysms present particularly acute medical risk due to the dangers associated with an inherently thin vascular wall. The utilization of vaso-occlusive devices to occlude an aneurysm without occluding the adjacent vasculature poses a special challenge. Methods, devices and materials that meet this challenge and still avoid undue risk of an aneurysm rupture are desirable.